Endocrine system : It consists of endocrine glands that secrete hormones directly into the circulatory system to be carried towards distant target organs.

Types of endocrine glands :

1. Pure endocrine glands : These glands only secrete hormones e.g. thyroid gland, pituitary gland etc.

2. Heterocrine glands : These glands secrete both enzymes and hormones. Thus, they act as endocrine and exocrine e.g. pancreas.